Gasoline filling station equipment typically comprises an underground fuel tank, a drop tube extending from the tank upwardly to a containment box with a containment valve at the containment box. The drop tube has long been intended to serve to reduce fumes emission.
Filling stations typically utilize individual customer dispensers for filling vehicle tanks. Vacuum assist systems have been provided to assist customers in maintaining effective sealing between dispensing nozzles and vehicle tank openings. Such systems provide a partial vacuum to assist such engagement. The vacuum system draws fuel fumes from the region of the dispensers in vehicle tanks to the underground tank.
The underground tank becomes pressurized by the cumulative effect of vapors produced therein, and from the filling of the tank via the drop tube by splashing and agitation. The build-up of vapors and pressure causes emission of vapors via the drop tube. Also, fuel vapors are produced and emitted at the containment box by any excess fluid therein. Fumes and vapor pressure prevent drainage of excess fluid via the drop tube to the tank. Pressure and vapors in the underground tank and the drop tube tend to prevent the drainage of excess fluid to the tank from the containment box, particularly when the gasoline or fuel is warmed, as on summer days when the temperature of the gasoline may be 85.degree.-90.degree.. The containment valve at the containment box is effectively inoperative when pressure is exerted therebelow. It is to be noted that it is illegal to operate any valve to relieve pressure in an underground tank of over 3" of water pressure.
Drop tubes of prior art systems typically terminate above the gasoline level in the underground tank, so that during input of fuel to the tank, splashing and agitation produce vapors and pressure in the tank which are emitted.
The present invention substantially prevents fumes emission by the provision of a drop tube which extends to a level below the surface of liquid fuel in the underground tank, thus eliminating fumes production by splashing and agitating the liquid fuel, particularly during filling operations and filling of the tank; fumes emission via the passage defined by the concentric drop tube and riser pipe by the sealing of the upper portions of the drop tube and riser pipe.